deecee, there are some slight differences in standard specifications but they overlap enough that the manufactures just make it to fit both specs today. It's kind of like buying 3.2% alcohol beer in the states that allowed the sale of 3.2% and under to younger people. The "adult" beer was supposed to be more than 3.2% but under 6%. Both beers were made to 3.2% and it was only the label that was different. But they couldn't have made it with that much control years ago when the laws were made.
And low carbon stainless steel, for improved weldability, is in the same category. Years ago, the manufacturers could not control or measure the amount of carbon in the steel that closely and had to make two different kinds of stainless steels, regular carbon and low carbon. Today's equipment makes this relatively easy and they make one product to fit both categories regularly.